Phase shift mask and manufacturing method thereof and exposure method using phase shift mask

ABSTRACT

A second light transmit portion of a phase shift mask is formed of a molybdenum silicide nitride oxide, or a molybdenum silicide oxide, or a chromium nitride oxide, or a chromium oxide, or a chromium carbide nitride oxide film converting a phase of transmitted exposure light by 180° and having the transmittance of at least 2% and less than 5%. In the manufacturing method of the second light transmit portion, a molybdenum silicide nitride oxide film, or a molybdenum silicide oxide film, or a chromium nitride oxide film, or a chromium oxide film, or a carbide nitride oxide film is formed by a sputtering method. Consequently, with a conventional sputtering apparatus, the second light transmit portion can be formed, and additionally, etching process of the phase shifter portion is required only once, so that probabilities of defects and errors in the manufacturing process can be decreased.

This application is a division of application Ser. No. 08/547,520 filedOct. 24, 1995, now U.S. Pat. No. 5,674,647, which is aContinuation-In-Part of application Ser. No. 08/155,370 filed Nov. 22,1993, now U.S. Pat. No. 5,474,864.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to phase shift masks, andparticularly to a structure of a phase shift mask of attenuation typeattenuating light intensity, and a method of manufacturing the same. Thepresent invention further relates to an exposure method using the phaseshift mask.

2. Description of the Background Art

Recently, high integration and miniaturization of a semiconductorintegrated circuit has been remarkably advanced, involvingminiaturization of a circuit pattern formed on a semiconductor substrate(hereinafter referred to simply as a wafer).

In particular, a photolithography technique is well known as a basictechnique in pattern formation. Although various developments andimprovements have been made, miniaturization of a pattern still keeps onadvancing, and a demand for enhancement of a pattern resolution has beenincreasing.

In general, a resolution limit R (nm) in a photolithography techniqueusing a reduction exposure method is described by the following:

    R=k.sub.1 ·λ/(NA)                          (1)

where λ is a wavelength (nm) of light to be used, NA is a numericalaperture of a lens, and K₁ is a constant which depends on a resistprocess.

As can be seen from the above expression, in order to enhance theresolution limit, K₁ and λ should be made smaller, and NA should be madelarger. That is, the wavelength should be decreased, and NA should beincreased, with the constant which depends on a resist process madesmaller.

However, improvement of a light source and a lens is technicallydifficult. In addition, a depth of focus δ (δ=k₂ ·λ/(NA)²) of light ismade smaller by decreasing the wavelength and increasing NA, whichrather leads to deterioration in the resolution.

Description will now be made of a cross section of a mask, an electricfield of exposure light on the mask, and light intensity on a wafer inusing a conventional photomask, with reference to FIGS. 44A, 44B, 44C.

First, the cross sectional structure of the mask will be described withreference to FIG. 44A. A metal mask pattern 2 of chromium or the like isformed on a glass substrate 1.

Referring to FIG. 44B, an electric field is generated along the maskpattern. Referring to FIG. 44C however, light beams passing through themask intensify each other at an overlaid portion of the light beamscaused by light diffraction and interference. Consequently, thedifference in the light intensity on the wafer becomes smaller, so thatthe resolution is deteriorated.

A phase shift exposure method with a phase shift mask has been proposedfor solving this problem, for example, in Japanese Patent Laying-OpenNos. 57-62052 and 58-173744.

The phase shift exposure method with a phase shift mask disclosed inJapanese Patent Laying-Open No. 58-173744 will now be described withreference to FIGS. 45A, 45B, 45C.

FIG. 45A shows a cross section of the phase shift mask. FIG. 45B showsan electric field on the mask. FIG. 45C shows light intensity on awafer.

First, referring to FIG. 45A, a phase shifter 6b of a transparentinsulation film such as a silicon oxide film is provided at every otheraperture portion 6a of a chromium mask pattern 2 formed on a glasssubstrate 1 to form a phase shift mask.

Referring to FIG. 45B, the electric field of a light beam passingthrough phase shifter 6b of the phase shift mask is inverted by 180°.

Therefore, the light beams transmitted through aperture portion 6a andthrough phase shifter 6b cancel each other on an overlaid portionthereof caused by a light interference effect. Consequently, as shown inFIG. 45C, the difference in the light intensity on the wafer issufficient for enhancing the resolution.

Although the aforementioned phase shift mask is very effective for aperiodical pattern such as lines and spaces, it cannot be set to anarbitrary pattern because complexity of the pattern causes greatdifficulty in arrangement of a phase shifter and the like.

As a phase shift mask solving the above problem, a phase shift mask ofattenuation type is disclosed, for example, in JJAP Series 5 Proc. of1991 Intern. Microprocess Conference pp. 3-9 and Japanese PatentLaying-Open No. 4-136854. Description will hereinafter be made of thephase shift mask of attenuation type disclosed in Japanese PatentLaying-Open No. 4-136854.

FIG. 46A is a cross section of the phase shift mask of attenuation type.FIG. 46B shows an electric field on the mask. FIG. 46C shows lightintensity on a wafer.

Referring to FIG. 46A, the structure of a phase shift mask 100 includesa quartz substrate 1 transmitting exposure light, and a phase shiftpattern 30 having a prescribed exposure pattern including a first lighttransmit portion 10 formed on a main surface of quartz substrate 1 andhaving the main surface exposed, and a second light transmit portion 20converting a phase of transmitted exposure light by 180° with respect tothe phase of exposure light transmitted through first light transmitportion 10.

Second light transmit portion 20 has a double layer structure includinga chromium layer 2 having the transmittance of 5-40% for exposure light,and a shifter layer 3 converting a phase of exposure light transmittedtherethrough by 180° with respect to that of exposure light transmittedthrough light transmit portion 10.

The electric field on the mask, of exposure light passing through phaseshift mask 100 having the above-described structure is as shown in FIG.46B. The light intensity on the wafer has its phase inverted at an edgeof the exposure pattern as shown in FIG. 46C.

The light intensity at an edge of the exposure pattern, therefore, isinvariably 0, as shown in the figure, so that the difference in theelectric field on light transmit portion 10 and phase shifter portion 20of the exposure pattern is sufficient for high resolution.

It should be noticed that the transmittance of second light transmitportion 20 for exposure light is set to 5-40% in the above method, forthe purpose of adjusting the thickness of the resist film afterdevelopment thereof by the transmittance, as shown in FIG. 31, so as toadapt the exposure amount appropriately for lithography.

Description will now be made of a method of manufacturing phase shiftmask 100. FIGS. 48 to 52 are cross sectional views showing themanufacturing steps according to the cross section of phase shift mask100 shown in FIG. 46A.

Referring to FIG. 48, chromium film 2 having the exposure lighttransmittance of 5-40% and the thickness of 50-200 Å, approximately, isformed on glass substrate 1. Thereafter, on chromium film 2 formed isSiO₂ film 3 of a prescribed thickness having the phase of exposure lightpassing therethrough converted by 180°. An electron beam resist film 5is formed on SiO₂ film 3.

Referring to FIG. 49, a predetermined portion of electron beam resistfilm 5 is exposed to electron beams and developed to form a resist 5having a desired pattern.

Referring to FIG. 50, with resist film 2 as a mask, the SiO₂ film isetched using a gas of the CHF₃ family. Referring to FIG. 51, chromiumfilm 2 is subjected to wet etching with resist film 5 and SiO₂ film 5 asa mask.

Referring to FIG. 52, phase shift mask 100 is completed by removingresist film 5.

In the above conventional technique, however, second light transmitportion 20 has a double layer structure including chromium film 2 forcontrolling the transmittance and SiO₂ film 3 for controlling the phasedifference. This structure, therefore, requires devices and processrespectively for formation of a chromium film and an SiO₂ film.

In addition, the chromium film and the SiO₂ film must be etchedseparately with different etching agents, resulting in numerous steps ofthe process, and thus leading to higher probabilities of defects and ofprocess errors in the pattern dimension.

Referring to FIG. 53, when a remaining defect (opaque defect) 50 and apinhole defect (clear defect) 51 should occur in the phase shift maskpattern, repairing methods respectively applicable to a chromium filmand an SiO₂ film will be required for repairing the defect. Aconventional repairing method, therefore, cannot be employed.

Referring to FIG. 54, according to an exposure method using theabove-described phase shift mask 100, the film thickness of a secondlight transmit portion 20 of phase shift mask 100 is approximately 3050Å to 4200 Å, which is relatively large. Therefore, as shown in thefigure, oblique exposure light out of exposure light from an exposurelight source has its phase not reliably converted by 180° even if ittransmits through second light transmit portion 20 of phase shift mask100. Exposure light having a different phase is produced.

SUMMARY OF THE INVENTION

One object of the present invention is to simplify manufacturing processof a phase shift mask, so as to provide a phase shift mask of highquality.

Another object of the present invention is to provide a manufacturingmethod of a phase shift mask having process simplified.

A still another object of the present invention is to provide anexposure method using a phase shift mask, which can prevent exposurefailure and improve the yield in the manufacturing steps of asemiconductor device.

In one aspect of the present invention, the phase shift mask includes asubstrate transmitting exposure light, and a phase shift pattern formedon a main surface of the substrate. The phase shift pattern includes afirst light transmit portion having the substrate exposed, and a secondlight transmit portion consisting of a single material having a phase oftransmitted exposure light converted by 180° with respect to the phaseof exposure light transmitted through the first light transmit portion,and having the transmittance of at least 2% and less than 5%.

The second light transmit portion is preferably formed of a singlematerial selected from the group consisting of an oxide of a metal, anitride oxide of metal, an oxide of a metal silicide and a nitride oxideof a metal silicide.

The second light transmit portion is preferably formed of a singlematerial selected form the group consisting of an oxide of chromium, anitride oxide of chromium, a carbide nitride oxide of chromium, an oxideof molybdenum silicide and a nitride oxide of molybdenum silicide.

The second light transmit portion is more preferably formed of a singlematerial selected from the group consisting of an oxide chromium, anitride oxide of chromium and a carbide nitride oxide of chromium.

The second light transmit portion preferably has the transmittancecontrolled through oxygen or nitrogen included therein, and the phasedifference controlled through the thickness thereof.

The exposure method using the phase shift mask according to the presentinvention includes the following steps.

First, a resist film is applied onto a pattern formation layer. Then,the resist film is exposed using a phase shift mask having a phase shiftpattern having a first light transmit portion formed on a substratetransmitting exposure light having the substrate exposed, and a secondlight transmit portion of a single material having a phase oftransmitted exposure light converted by 180° with respect to the phaseof exposure light transmitted through the first light transmit portion,and having the transmittance of at least 2% and less than 5%

As a result, it is possible to form a thin second light transmit portionof the thickness of approximately 1500 Å to 2000 Å, and to convert thephase of oblique exposure light by 180°. Therefore, exposure light hasits phase uniformed after transmitting through the second light transmitportion of the phase shift mask, making it possible to prevent occurrentof exposure failure. Consequently, the yield can be improved in themanufacturing steps of a semiconductor device.

In accordance with the present invention, the method of manufacturing aphase shift mask includes the following steps.

A phase shifter film of a prescribed thickness having a phase oftransmitted exposure light converted by 180°, and having thetransmittance of at least 2% and less than 5% is formed on a substratetransmitting exposure light by a sputtering method. A resist film of aprescribed pattern is formed on the phase shifter film.

With the resist film as a mask, the phase shifter film is etched by adry etching method, so that a first light transmit portion having thesubstrate exposed and a second light transmit portion formed of thephase shifter film are formed.

The step of forming the phase shifter film preferably includes the stepof forming a molybdenum silicide oxide film with a molybdenum silicidetarget in a mixed gas atmosphere of argon and oxygen.

The mixed gas preferably includes 73-76% argon gas, and an oxygen gas ofthe remaining percent by volume.

The step of forming the phase shifter film preferably includes the stepof forming a molybdenum silicide nitride oxide film with a molybdenumsilicide target in a mixed gas atmosphere of an argon gas, an oxygen gasand a nitrogen gas.

The mixed gas preferably includes 57-79% argon gas, 7-18% oxygen gas,and 4-32% nitrogen gas by volume.

The step of forming the phase shifter film preferably includes the stepof forming a chromium oxide film with a chromium target in a mixed gasatmosphere of argon and oxygen.

The mixed gas includes 95-96% argon gas, and an oxygen gas of theremaining percent by volume.

The step of forming the phase shifter film preferably includes the stepof forming a chromium nitride film with a chromium target in a mixed gasatmosphere of argon, oxygen and nitrogen.

The mixed gas preferably includes 82-83% argon gas, 4-5% oxygen, and12-13% nitrogen by volume.

The step of forming the phase shifter film preferably includes the stepof forming a chromium nitride oxide film with a chromium target in amixed gas atmosphere of argon and nitrogen monoxide.

The mixed gas includes 75-87% argon gas, and nitrogen monoxide of theremaining percent by volume.

The step of forming the phase shifter film preferably includes the stepof forming a chromium carbide nitride oxide film with a chromium targetin a mixed gas atmosphere of argon, oxygen and methane.

The mixed gas preferably includes 78-79% argon gas, 12-14% oxygen, and8-9% methane by volume.

The step of forming the phase shift mask preferably includes the step offorming an antistatic film.

The step of forming the antistatic film preferably includes the step offorming a molybdenum film by a sputtering method between the steps offorming the phase shifter film and forming the resist film.

The step of forming the antistatic film preferably includes the step offorming a chromium film by a sputtering method between the steps offorming the phase shifter film and forming the resist film.

The step of etching the phase shifter film is preferably performed by adry etching method with a mixed gas of carbon fluoride and oxygen.

The step of etching the phase shifter film is preferably performed by adry etching method with a gas selected from the group consisting of amixed gas of methylene chloride and oxygen, a mixed gas of chlorine andoxygen, and a chlorine gas.

The step of forming the phase shifter film preferably includes the stepof performing heating process at or above 200° C. after forming thephase shifter film by a sputtering method.

As described above, in the phase shift mask and the manufacturing methodthereof in accordance with the present invention, the second lighttransmit portion is formed of a single material film.

In the manufacturing process of the phase shifter, a film of aprescribed single material is formed on a substrate transmittingexposure light by a sputtering method, and thereafter, a second lighttransmit portion is formed by prescribed etching.

This enables formation of a phase shift portion with a conventionalsputtering device, and also enables etching of a phase shifter portionwith a single etching agent.

Consequently, the steps of forming a phase shifter film and etching thesame are required only once, respectively, in the manufacturing process,so that probabilities of defects and of process errors in the patterndimension can be reduced, and thus a phase shift mask of high qualitycan be provided.

In addition, since a second light transmit portion is formed of a singlematerial film, a defective portion can be readily repaired by aconventional method.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a phase shift mask in a firstembodiment according to the present invention.

FIG. 2A is a cross sectional view of a phase shift mask according to thepresent invention. FIG. 2B is a schematic diagram showing an electricfield of exposure light on the mask. FIG. 2C is a schematic diagramshowing light intensity on a wafer.

FIGS. 3 to 6 are cross sectional views showing the first to fourth stepsof the manufacturing method of the phase shift mask in the firstembodiment according to the present invention.

FIG. 7 is a schematic diagram showing the structure of a DC magnetronsputtering apparatus.

FIG. 8 is a graph showing the relation of n value, k value and a filmthickness in using a krF laser.

FIG. 9 is a graph showing the relation of n value, k value and a filmthickness in using an i-line.

FIG. 10 is a graph showing the relation of n value, k value and a filmthickness in using a g-line.

FIG. 11 is a plot showing case by case a flow ratio of a mixed gas information of the phase shifter film in the first embodiment.

FIGS. 12 to 15 are cross sectional views showing the first to fourthsteps of the manufacturing method of a phase shift mask in a secondembodiment according to the present invention.

FIG. 16 is a graph showing the relation of n value, k value and a filmthickness in using KrF laser.

FIG. 17 is a graph showing the relation of n value, k value and a filmthickness in using an i-line.

FIG. 18 is a graph showing the relation of n value, k value and a filmthickness in using a g-line.

FIG. 19 is a first diagram plotting case by case a flow ratio of a mixedgas in formation of the phase shifter film in the second embodiment.

FIG. 20 is a second diagram plotting case by case a flow ratio of amixed gas in formation of the phase shifter film in the secondembodiment.

FIG. 21 is a third diagram plotting case by case a flow ratio of a mixedgas in formation of the phase shifter film in the second embodiment.

FIGS. 22 to 26 are cross sectional views showing the first to fifthsteps of the manufacturing method of a phase sift mask in a thirdembodiment according to the present invention.

FIG. 27 is a cross sectional view showing a defect repairing method of aphase shift mask according to the present invention.

FIG. 28 is a schematic diagram showing a state of an exposure methodusing the phase shift mask according to the present invention.

FIG. 29 is a graph showing the relationship between focus offset andcontact hole size in the exposure method using the phase shift maskaccording to the present invention.

FIG. 30 is a graph showing the relationship between focus offset andcontact hole size in the exposure method using a photomask in aconventional technique.

FIG. 31 is a graph showing a comparison of the relationship betweencoherence and depth of focus of the exposure method using the phaseshift mask according to the present invention with that of the exposuremethod using a phase shift mask in a conventional technique.

FIG. 32 is a cross sectional view showing a structure of a phase shiftmask of attenuation type.

FIG. 33 shows light intensity of the light transmitting through thephase shift mask of attenuation type shown in FIG. 32.

FIG. 34 is a cross sectional view showing a structure of a resist filmformed by using the phase shift mask of attenuation type shown in FIG.32.

FIG. 35 shows a two-dimensional structure of the resist film formed byusing the phase shift mask of attenuation type shown in FIG. 32.

FIG. 36 is a plan view of a phase shift mask of attenuation type inwhich a first light transmit portion has a line pattern.

FIG. 37 is a plan view showing a structure of the resist film formed byusing the phase shift mask of attenuation type shown in FIG. 36.

FIG. 38 is a graph showing the relation between transmittance T (%) anddepth of focus (DOF).

FIG. 39 shows a comparison between the depth of focus of a normalphotomask and that of the phase shift mask having the transmittance of1, 3, 5% based on the data shown in FIG. 38.

FIGS. 40-43 are first through fourth diagrams each plotting case by casea flow ratio of a mixed gas in formation of the phase shifter film inthe fourth embodiment.

FIG. 44A is a cross sectional view of a photomask in a conventionaltechnique. FIG. 44B is a schematic diagram showing an electric field ofexposure light on the mask. FIG. 44C is a schematic diagram showinglight intensity on a wafer.

FIG. 45A is a cross sectional view of a phase shift mask in aconventional technique. FIG. 45B is a schematic diagram showing anelectric field of exposure light on the mask. FIG. 45C is a schematicdiagram showing light intensity on a wafer.

FIG. 46A is a cross sectional view of a phase shift mask in aconventional technique. FIG. 46B is a schematic diagram showing anelectric field of exposure light on the mask. FIG. 46C is a schematicdiagram showing light intensity on a wafer.

FIG. 47 is a graph showing the relation between a transmittance ofexposure light and a thickness of a resist film.

FIGS. 48 to 52 are cross sectional views showing the first to fifthsteps of a manufacturing method of a phase shift mask in a conventionaltechnique.

FIG. 53 is a cross sectional view showing a problem of the phase shiftmask in the conventional technique.

FIG. 54 is a diagram showing a problem of the exposure method using aphase shift mask in a conventional technique.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment in accordance with the present invention willhereinafter be described.

First, description will be made of the structure of phase shift mask inthis embodiment with reference to FIG. 1. A phase shift mask 200includes a quartz substrate 1 transmitting exposure light, and a phaseshift pattern 30 formed on a main surface of quartz substrate 1. Phaseshift pattern 30 includes a first light transmit portion 10 havingquartz substrate 1 exposed, and a second light transmit portion 4 of asingle material having a phase of transmitted exposure light convertedby 180° with respect to the phase of exposure light transmitted throughfirst light transmit portion 10, and having the transmittance of 5-40%.

Description will be made of an electric field of exposure light passingtherethrough on phase shift mask 200 of the above structure, and lightintensity on a wafer with reference to FIGS. 2A, 2B, 2C.

FIG. 2A is a cross sectional view of phase shift mask 200 describedabove. Referring to FIG. 2B, since the electric field on the mask isinverted at an edge of a exposure pattern, the electric field at theedge portion of the exposure pattern is invariably zero. Accordingly, asshown in FIG. 2c, the difference in the electric field on the wafer atlight transmit portion 10 and at phase shift portion 4 of the exposurepattern is sufficient for obtaining higher resolution.

It should be noticed that the transmittance of second light transmitportion 4 is set to 5-40% for the purpose of adjusting the thickness ofa resist film after development to adapt appropriately the exposureamount for lithography.

Description will now be made of a manufacturing method of phase shiftmask 200 in a second embodiment, employing a molybdenum silicide oxidefilm or a molybdenum silicide nitride oxide film as a phase shifterfilm.

FIGS. 3 to 6 are cross sectional views showing the manufacturing processof phase shift mask 200 shown in FIG. 1.

Referring to FIG. 3, on a quartz substrate 1 formed is a phase shifterfilm 4 of a molybdenum silicide oxide film or a molybdenum silicidenitride oxide film by a sputtering method.

Thereafter, in order to stabilize the transmittance of phase shifterfilm 4, heating process is performed at or above 200° C. suing a cleanoven or the like.

Consequently, fluctuation of the transmittance (0.5-1.0%) conventionallycaused by heating process such as resist application process(approximately 180° C.) in formation of a phase shifter film can beprevented.

Subsequently, an electron beam resist film 5 (EP-810S (registeredtrademark) manufactured by Nihon Zeon) of approximately 5000 Å inthickness is formed on phase shifter film 4. Since the molybdenumsilicide oxide film or molybdenum silicide nitride oxide film does nothave conductivity, an antistatic film 6 (Espacer 100 (registeredtrademark) manufactured by Showa Denko) of approximately 100 Å is formedthereon for prevention of being charged in irradiation of electronbeams.

Referring to FIG. 4, electron beam resist film 5 is irradiated withelectron beams, and thereafter, antistatic film 6 is washed away withwater. Resist film 5 having a prescribed resist pattern is then formedby development of resist film 5.

Referring to FIG. 5, phase shifter film 4 is etched with resist film 5as a mask. At this time, an RF ion etching apparatus of horizontal flatplate type is employed, which performs etching for approximately elevenminutes under the conditions of the electrode-substrate distance of 60mm, the operating pressure of 0.3 Torr, and the flow rates of reactiongases CF₄ and O₂ of 95 sccm and 5 sccm, respectively.

Referring to FIG. 6, resist 5 is removed. Through these steps, the phaseshift mask in accordance with the present embodiment is completed.

Formation of the phase shifter film utilizing the above-describedsputtering method will hereinafter be described in detail. To have thetransmittance for exposure light within the range of 5-40%, and toconvert a phase of exposure light by 180° are the requirements for aphase shift film.

As a film satisfying these conditions, therefore, a film made of amolybdenum silicide nitride oxide was employed in the presentembodiment.

Description will be made of a sputtering apparatus for forming theaforementioned film with reference to FIG. 7.

FIG. 7 is a schematic diagram showing the structure of a DC magnetronsputtering apparatus 500.

DC magnetron sputtering apparatus 500 includes a vacuum vessel 506provided with a magnetron cathode 509 including a target 507 and amagnet 508 therein.

An anode 510 is provided opposed to and spaced by a predetermineddistance from target 507, on the opposite surface of which from target507 provided is a quartz substrate 1 of 2.3 mm in thickness and 127 mmsquare, for example.

An exhaust pipe 512 and a gas feed pipe 513 are provided atpredetermined positions of vacuum vessel 506. In formation of a film,molybdenum silicide is used as a target, and the temperature of quartzsubstrate 1 is held at 60°-150° C. by a heater and a temperaturecontroller, not shown.

Under these conditions, argon as a sputter gas and a mixed gas of oxygenand nitrogen as reaction gas are introduced from gas feed pipe 513 at aprescribed rate, the pressure in vacuum vessel 506 is held at aprescribed value, and a direct current voltage is applied betweenelectrodes.

In this embodiment, phase shifter films of a molybdenum silicide oxideand of a molybdenum silicide nitride oxide were formed in variousconditions.

Table 1 shows the pressure in vacuum vessel 506, the deposition rate andthe film material in each of the cases in which various flow ratios ofthe mixed gas are set. A phase shifter film of a molybdenum silicidenitride oxide is to be formed in Cases M-1 to M-7, M-14, and M-15, whilea phase shifter film of a molybdenum silicide oxide is to be formed inCases M-8 to M-13, M-16, and M-17.

Tables 2-4 are graphs showing the transmittance, the n value and the kvalue in an optical constant (n-i·k), and the film thickness d_(s). forconverting a phase of exposure light by 180°, in the cases employing akrF laser (λ=248 nm), an i-line (λ=365 nm) and a g-line (λ=436 nm) asexposure light, respectively.

In Tables 2-4, the film thickness d_(s) can be obtained from thefollowing:

    d.sub.s =λ/2(n-1)                                   (2)

where λ is a wavelength of exposure light, and n is a value in theoptical constant.

                  TABLE 1                                                         ______________________________________                                        gas flow ratio    pressure                                                                              deposition                                          %                 ×10.sup.-3                                                                      rate       film                                     case Ar       O.sub.2                                                                              N.sub.2                                                                              Torr  Å/min                                                                              material                           ______________________________________                                        M-1  72.6     23.8   3.6    2.0   709      MoSi                               M-2  77.1     18.3   4.6    2.0   645      nitride                            M-3  72.1     8.6    19.3   2.0   600      oxide                              M-4  68.6     7.9    23.5   2.1   525      film                               M-5  61.4     7.0    31.6   2.1   486                                         M-6  57.4     13.1   29.5   2.2   522                                         M-7  65.4     17.8   16.8   2.0   578                                         M-8  79.5     20.5   0      2.0   635      MoSi                               M-9  73.3     26.7   0      2.0   600      oxide                              M-10 78.8     21.2   0      2.6   225      film                               M-11 81.1     18.9   0      2.6   632                                         M-12 82.3     17.7   0      2.6   650                                         M-13 83.5     16.5   0      2.6   754                                         M-14 73.4     14.9   11.7   3.0   702      MoSi                               M-15 79.0     16.8   4.2    2.8   750      nitride                                                                       oxide                                                                         film                               M-16 76.0     24.0   0      2.6   830      MoSi                               M-17 92.0     8.0    0      5.5   487      oxide                                                                         film                               ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        krF laser (wavelength 248 nm)                                                 transmittance  optical constant                                                                           ##STR1##                                          case    %         n        k     Å                                        ______________________________________                                        M-1     5.22      1.195    0.409 1355                                         M-2     3.59      1.860    0.437 1442                                         M-3     2.92      1.986    0.530 1258                                         M-4     0.69      2.14     0.868 1088                                         M-5     0.74      2.09     0.821 1137                                         M-6     1.8       1.922    0.569 1345                                         M-7     2.6       1.963    0.538 1288                                         M-8     7.0       1.79     0.318 1570                                         M-9     4.6       1.68     0.322 1824                                         M-10    10.2      1.730    0.251 1700                                         M-11    5.0       1.76     0.350 1630                                         M-12    6.13      1.91     0.384 1360                                         M-13    5.51      1.90     0.394 1380                                         M-14    3.52      2.054    0.5325                                                                              1176                                         M-15    3.03      2.111    0.5855                                                                              1116                                         M-16    4.39      1.804    0.3844                                                                              1541                                         M-17    6.88      1.842    0.3409                                                                              1472                                         ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        i-line (wavelength 365 nm)                                                    transmittance  optical constant                                                                           ##STR2##                                          case    %         n        k     Å                                        ______________________________________                                        M-1     11.6      1.874    0.280 2088                                         M-2     11.5      1.950    0.304 1921                                         M-3     8.82      2.11     0.397 1644                                         M-4     2.9       2.318    0.697 1382                                         M-5     4.15      2.344    0.626 1362                                         M-6     3.5       2.01     0.511 1807                                         M-7     4.53      1.88     0.414 2074                                         M-8     44.5      2.11     0.118 1644                                         M-9     78.6      1.85     0.0169                                                                              2147                                         M-10    73.8      1.77     0.020 2370                                         M-11    18.7      1.91     0.222 2005                                         M-12    12.2      1.81     0.254 2250                                         M-13    17.9      1.98     0.245 1860                                         M-14    8.55      2.068    0.389 1709                                         M-15    8.71      2.189    0.420 1535                                         M-16    9.39      1.707    0.2536                                                                              2581                                         M-17    16.5      1.833    0.2207                                                                              2192                                         ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        g-line (wavelength 436 nm)                                                    transmittance  optical constant                                                                           ##STR3##                                          case    %         n        k     Å                                        ______________________________________                                        M-1     12.0      1.786    0.249 2774                                         M-2     16.4      2.006    0.265 2167                                         M-3     11.7      2.148    0.358 1900                                         M-4     3.9       2.346    0.644 1620                                         M-5     3.4       2.121    0.572 1945                                         M-6     4.4       1.860    0.410 2535                                         M-7     8.8       2.018    0.367 2141                                         M-8     46.3      2.197    0.114 1821                                         M-9     83.0      1.795    0.0069                                                                              2742                                         M-10    78.0      1.733    0.0123                                                                              2974                                         M-11    22.2      1.901    0.195 2420                                         M-12    21.1      1.982    0.220 2220                                         M-13    13.3      1.702    0.213 3105                                         M-14    13.0      2.124    0.3325                                                                              1940                                         M-15    11.9      2.185    0.3653                                                                              1840                                         M-16    17.9      1.886    0.222 2460                                         M-17    18.2      1.775    0.1934                                                                              2812                                         ______________________________________                                    

FIGS. 8 to 10 are graphs of data shown in Table 2 to 4, respectively, inwhich the horizontal axis indicates the n value in the optical constant,the left vertical axis indicates the k value in the optical constant,and the right vertical axis indicates the film thickness d_(s).

The transmittance T is also shown in FIGS. 8 to 10.

Referring to FIG. 8 showing the cases of exposure light of the krFlaser, it can be seen that the transmittance T within the range of 5-40%required for a phase shifter film is obtained in M-1, M-8, M-10 to M-13,and M-17.

Referring to FIG. 9 showing the cases of exposure light of the i-line,the transmittance T within the range of 5-40% required for a phase shiftmask is obtained in M-1 to M-3, M-8, and M-11 to M-17.

Referring to FIG. 10 showing the cases of exposure light of the g-line,it can be seen that the transmittance T within the range of 5-40%required for a phase shifter film is obtained in M-1 to M-3, M-7, andM-11 to M-17.

As a result, the films formed in M-1 to M-3, M-7, M-8, and M-10 to M-17can be employed as a phase shifter film.

FIG. 11 is a graph showing the above cases with respect to gas flowratios. In the graph shown in FIG. 11, respective rates of argon, oxygenand nitrogen in Cases M-1 to M-17 are described.

In this graph, a point of a mixed gas in each case is plotted, whereinthe base of the triangle indicates the flow ratio (%) of argon, the leftoblique side thereof indicates the flow ratio (%) of oxygen, and theright oblique side thereof indicates the flow ratio (%) of nitrogen. Inaccordance with the result shown in FIGS. 8 to 10, a case the film ofwhich is applicable as a phase shifter film is indicated by a circle,while a case the film of which is not applicable to a phase shifter filmis indicated by a cross.

As can be seen from the graph in FIG. 11, a mixed gas for forming amolybdenum silicide oxide film applicable as a phase shifter filmincludes 76-92% argon and 8-24% oxygen by volume.

A mixed gas for forming a molybdenum silicon nitride oxide filmapplicable as a phase shifter film includes 65-79% argon, 8-24% oxygen,and 3-20% nitrogen by volume.

The upper limit of oxygen is set to 35%, because the rate occupied byoxygen of 50% or more will cause deposition of an oxide on an electrodein the sputtering apparatus, thereby preventing sputtering. It is thusdefined by the restriction of the apparatus.

As described above, in the phase shift mask in accordance with thepresent invention, a second light transmit portion is constituted onlyof a molybdenum silicide oxide film or a molybdenum silicide nitrideoxide film having the transmittance of 4-50%.

In the manufacturing process thereof, a molybdenum silicon oxide or amolybdenum silicide nitride oxide is formed to a prescribed filmthickness by a sputtering method, and thereafter, a prescribed etchingis performed, whereby the second light transmit portion is formed.

Consequently, a phase shifter film can be formed with a conventionalsputtering apparatus, and additionally, probabilities of defects anderrors in a pattern dimension can be reduced because etching process isrequired only once.

Description will hereinafter be made of a method of manufacturing phaseshift mask 200 in accordance with a third embodiment, where either of achromium oxide film, a chromium nitride oxide film, and a chromiumcarbide nitride oxide film is employed as a phase shifter film.

FIGS. 12 to 15 are cross sectional views showing the manufacturing stepsof phase shift mask 200 shown in FIG. 1.

Referring to FIG. 12, phase shifter film 4 of a chromium oxide film, achromium nitride oxide film, or a chromium carbide nitride oxide isformed on quartz substrate 1 by a sputtering method.

In order to stabilize the transmittance of phase shifter film 4, heatingprocess is performed at approximately 200° C. or more with a clean ovenor the like.

This prevents fluctuation of the transmittance (0.5-1.0%) cause byconventional heating processing (approximately 180° C.) in resistapplication process after phase shifter film formation.

Subsequently, a resist film 5 of approximately 5000 Å in thickness isformed on phase shifter film 4.

Referring to FIG. 13, resist film 5 is irradiated with an i-line anddeveloped so as to have a prescribed resist pattern.

Referring to FIG. 14, phase shifter film 4 is etched with resist film 5as a mask. At this time, an RF ion etching apparatus of horizontal flatplate type is employed, in which etching is performed for approximatelyfour minutes under the conditions of the electrode-substrate distance of100 mm, the operating pressure of 0.3 Torr, the flow rates of reactiongases CH₂ Cl₂ and O₂ of 25 sccm and 75 sccm, respectively. The phaseshift mask in accordance with the present embodiment is thus completed.

Detailed description will now be made of formation of the phase shiftmask utilizing the sputtering method described above. To have thetransmittance within the range of 5-40% for exposure light, and toconvert of a phase of exposure light by 180° are the requirements for aphase shifter film.

As a film satisfying these conditions, therefore, a film made of achromium oxide, a chromium nitride oxide, or a chromium carbide oxidenitride is employed in the present embodiment.

The structure of the sputtering apparatus for forming the above phaseshifter film is the same as that shown in FIG. 7, and the descriptionthereof is not repeated.

In the present embodiment, phase shift masks of a chromium oxide film, achromium nitride oxide film, and a chromium carbide nitride oxide filmwere formed in various cases.

Table 5 shows the pressure in vacuum vessel, the deposition rate and thefilm material in each of the cases in which various flow ratios of amixed gas are set. A phase shifter film of a chromium oxide is to beformed in Cases C-1 to C-13, a phase shifter film of a chromium nitrideoxide is to be formed in Cases C-14 to C-26, and a phase shifter film ofa chromium carbide nitride oxide is to be formed in Cases C-27 to C-30.

Tables 6 to 8 are graphs showing the transmittance, the n value and thek value in the optical constant (n-i·k), and the film thickness d_(s)for converting a phase of exposure light by 180° in the cases employinga krF laser (λ=248 nm), an i-line (λ=365 nm) and a g-line (λ=436 nm),respectively.

In Tables 6 to 8, the film thickness d_(s) can be obtained from thefollowing:

    d.sub.s =λ/2(n-1)                                   (2)

where λ is a wavelength of exposure light, and n is a value in theoptical constant.

                  TABLE 5                                                         ______________________________________                                        gas flow ratio      pressure                                                                              deposition                                        %                   ×10.sup.-3                                                                      rate     film                                     case Ar     O.sub.2                                                                              N.sub.2                                                                            NO   CH.sub.4                                                                           Torr  Å/min                                                                            material                       ______________________________________                                        C-1  71.4   28.6   0    0    0    3.0   259    Cr                             C-2  92.3   7.7    0    0    0    3.9   850    oxide                          C-3  90.0   10.0   0    0    0    3.0   900    film                           C-4  85.0   15.0   0    0    0    2.0   941                                   C-5  85.5   14.5   0    0    0    6.1   796                                   C-6  89.3   10.7   0    0    0    8.0   828                                   C-7  92.7   7.3    0    0    0    4.0   758                                   C-8  96.6   3.4    0    0    0    4.0   448                                   C-9  94.8   5.2    0    0    0    8.1   733                                   C-10 93.1   6.9    0    0    0    6.1   791                                   C-11 90.2   9.81   0    0    0    4.0   824                                   C-12 90.1   9.93   0    0    0    4.1   787                                   C-13 95.1   4.92   0    0    0    8.2   659                                   C-14 54.1   32.4   13.5 0    0    1.5   110    Cr                             C-15 48.8   39.0   12.2 0    0    1.5   108    nitride                        C-16 87.2   6.4    6.4  0    0    4.1   592    oxide                          C-17 82.9   4.9    12.2 0    0    4.2   523    film                           C-18 90.0   1.3    8.7  0    0    4.1   756                                   C-19 76.0   0      0    24.0 0    2.0   600                                   C-20 83.0   0      0    17.0 0    3.2   620                                   C-21 75.5   0      0    24.5 0    2.3   570                                   C-22 86.0   0      0    14.0 0    4.2   550                                   C-23 86.5   0      0    13.5 0    4.1   580                                   C-24 82.4   0      0    17.6 0    3.2   520                                   C-25 86.2   0      0    13.8 0    4.2   129                                   C-26 87.1   0      0    12.9 0    4.1   675                                   C-27 85.2   5.3    0    0    9.5  4.0   471    Cr                             C-28 82.9   7.9    0    0    9.2  3.0   513    carbide                        C-29 78.3   13.0   0    0    8.7  2.0   642    nitride                        C-30 87.9   2.3    0    0    9.8  8.1   399    oxide                                                                         film                           ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        krF laser (wavelength 248 nm)                                                 transmittance optical constant                                                                            ##STR4##                                          case    %         n        k     Å                                        ______________________________________                                        C-1     8.9       2.782    0.5696                                                                              696                                          C-13    3.50      2.538    0.7448                                                                              806.2                                        C-25    3.80      2.565    0.7347                                                                              792                                          ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        i-line (wavelength 365 nm)                                                    transmittance optical constant                                                                            ##STR5##                                          case    %         n        k     Å                                        ______________________________________                                        C-1     31.7      2.23     0.187 1484                                         C-2     8.95      2.529    0.5108                                                                              1194                                         C-3     6.08      2.355    0.5495                                                                              1347                                         C-4     6.52      2.481    0.5749                                                                              1212                                         C-5     5.81      2.258    0.5252                                                                              1451                                         C-6     5.64      2.272    0.5364                                                                              1435                                         C-7     6.18      2.275    0.5186                                                                              1432                                         C-8     6.22      2.225    0.5000                                                                              1490                                         C-9     12.9      2.513    0.4171                                                                              1238                                         C-10    8.52      2.296    1.4603                                                                              1408                                         C-11    6.63      2.238    0.4922                                                                              1474                                         C-12    7.23      2.299    0.8949                                                                              1405                                         C-13    11.3      2.579    0.4634                                                                              1159                                         C-14    9.79      2.44     0.468 1267                                         C-15    10.0      2.50     0.476 1217                                         C-16    5.35      2.527    0.6365                                                                              1195                                         C-17    4.65      2.494    0.6588                                                                              1222                                         C-18    8.78      2.632    0.5399                                                                              1118                                         C-19    0.199     2.142    1.098 1598                                         C-20    0.543     2.283    1.089 1250                                         C-21    1.42      2.316    0.8407                                                                              1387                                         C-22    1.60      2.346    0.8336                                                                              1100                                         C-23    0.102     2.290    1.3672                                                                              1415                                         C-24    1.38      2.413    0.9021                                                                              1100                                         C-25    12.1      2.471    0.4257                                                                              1241                                         C-26    1.80      2.505    0.8904                                                                              1213                                         C-27    6.18      2.530    0.6010                                                                              1196                                         C-28    5.06      2.283    0.5625                                                                              1422                                         C-29    3.47      2.440    0.7066                                                                              1267                                         C-30    8.65      2.413    0.4894                                                                              1291                                         ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        g-line (wavelength 436 nm)                                                    transmittance optical constant                                                                            ##STR6##                                          case    %         n        k     Å                                        ______________________________________                                        C-2     19.58     2.660    0.3262                                                                              1313                                         C-3     14.2      2.365    0.3689                                                                              1597                                         C-4     11.1      2.285    0.4029                                                                              1696                                         C-5     17.3      2.595    0.3495                                                                              1411                                         C-6     16.1      2.538    0.3669                                                                              1417                                         C-7     19.73     2.629    0.3220                                                                              1338                                         C-8     21.9      2.630    0.2936                                                                              1537                                         C-9     27.1      2.590    0.2343                                                                              1371                                         C-10    25.3      2.900    0.2514                                                                              1147                                         C-11    21.2      2.539    0.297 1416                                         C-12    20.8      2.617    0.3062                                                                              1348                                         C-13    23.4      2.676    0.2760                                                                              1301                                         C-16    14.4      2.786    0.4263                                                                              1221                                         C-17    12.5      2.732    0.4621                                                                              1258                                         C-18    9.94      2.053    0.3587                                                                              2070                                         C-19    1.93      2.607    0.925 1356                                         C-21    2.84      2.706    0.8715                                                                              1270                                         C-22    6.13      2.706    0.6562                                                                              1280                                         C-23    3.60      2.631    0.7820                                                                              1320                                         C-24    5.02      2.748    0.7250                                                                              1250                                         C-26    3.98      2.630    0.7475                                                                              1337                                         C-27    1.29      1.731    0.4952                                                                              2982                                         C-28    14.5      2.482    0.3834                                                                              1471                                         C-29    5.50      2.335    0.5641                                                                              1633                                         C-30    18.8      2.580    0.3304                                                                              1380                                         ______________________________________                                    

FIGS. 16, 17 and 18 are graphs of data shown in Tables 6, 7 and 8. Thehorizontal axis indicates the n value in the optical constant, the leftvertical axis indicates the k value in the optical constant, and theright vertical axis indicates the film thickness d_(s).

The transmittance T is also shown in FIGS. 16, 17 and 18.

Referring to FIG. 17 showing the case of exposure light of the i-line,it can be seen that the transmittance T within the range of 5-40%required for a phase shift mask is obtained in C-1 to C-16, C-18, C-25,C-27, C-28, and C-30.

Referring to FIG. 18 showing the case of exposure light of the g-line,it can be seen that the transmittance T within the range of 5-40%required for a phase shift mask is obtained in Cases C-2 to C-13, C-16to C-18, C-22, C-24, and C-28 to C-30.

As a result, the films formed in Cases C-1 to C-18, C-22, C-24, C-25,and C-27 to C-30 can be employed as a phase shifter film.

FIGS. 19 to 21 are graphs showing the above cases based on the relationof gas flow ratios in mixed gases Ar+O₂ ; Ar+O₂ +N₂, Ar+NO, and Ar+O₂+CH₄, respectively.

The graph of FIG. 19 shows the rates of argon, oxygen and nitrogen inCases C-1 to C-18.

In this graph, a point of a mixed gas in each case is plotted, whereinthe base of the triangle indicates the flow ratio (%) of argon, the leftoblique side of the triangle indicates the flow ratio (%) of oxygen, andthe right oblique side of the triangle indicates the flow ratio (%) ofnitrogen.

In accordance with the result in FIGS. 16, 17 and 18, a case the film ofwhich is applicable as a phase shifter film is indicated by a circle,while a case the film of which is. not applicable as a phase shifterfilm is indicated by a cross.

As can be seen from the graph of FIG. 19, a mixed gas for forming achromium oxide film applicable as a phase shifter film includes 48-97%argon and 3-39% oxygen by volume.

A mixed gas for forming a chromium nitride oxide film applicable as aphase shifter film includes 48-90% argon, 1-39% oxygen, and 6-14%nitrogen by volume.

The upper limit of oxygen is set to 39%, because the rate occupied byoxygen of 50% or more will cause deposition of an oxide on an electrodein the sputtering apparatus, thereby preventing sputtering. It is thusdefined by the restriction of the apparatus.

FIG. 20 is a graph showing the rates of argon and NO in Cases C-19 toC-26. In accordance with the results in FIGS. 16, 17 and 18, a case thefilm of which is applicable as a phase shift mask is indicate by acircle, while a case the film of which is not applicable as a phaseshifter mask is indicated by a cross.

FIG. 21 is a graph showing the rates of argon, oxygen and methane inCases C-27 to C-30.

In the graph, a point of a mixed gas in each case is plotted, whereinthe base of the triangle indicates the flow ratio (%) of argon, the leftoblique side thereof indicates the flow ratio (%) of oxygen, and theright oblique side thereof indicates the flow ratio (%) of methane.

In accordance with the result in FIGS. 16, 17 and 18, a case the film ofwhich is applicable as a phase shifter film is indicated by a circle,while a case the film of which is not applicable as a phase shifter filmis indicated by a cross.

As can be seen from the graphs in FIGS. 20 and 21, a mixed gas forforming a chromium nitride oxide film applicable as a phase shifter filmincludes 82-87% argon, and 13-18% nitrogen monoxide by volume.

A mixed gas for forming a chromium carbide nitride oxide film applicableas a phase shifter film includes 78-88% argon, 2-13% oxygen and 8-10%methane by volume.

As described above, in the phase shift mask in accordance with thepresent embodiment, a second light transmit portion is constituted onlyof a film of a chromium oxide, a chromium nitride oxide, or a chromiumcarbide nitride oxide, having the transmittance of 4-50%.

In the manufacturing process thereof, a film of a chromium oxide, achromium nitride oxide, or a chromium carbide nitride oxide is formed toa prescribed film thickness by a sputtering method, and thereafter, aprescribed etching is performed, so that the second light transmitportion is formed.

Consequently, a phase shifter film can be formed with a conventionalsputtering apparatus, and probabilities of defects and errors in apattern dimension can be reduced since etching process is required onlyonce.

Although an oxide and a nitride oxide of molybdenum silicide, and anoxide, a nitride oxide, and a carbide nitride oxide of chromium are usedas the second light transmit portion in the second and thirdembodiments, it is not limited to them, and an oxide and a nitride ofmetal, and an oxide and a nitride oxide of metal silicide may be used.

Description will now be made of a fourth embodiment in accordance withthe present invention. In the present embodiment, an antistatic metalfilm is formed for prevention of being charged in irradiation ofelectron beams or laser beams on a phase shifter film in themanufacturing process thereof.

The manufacturing process of the phase shifter film will be describedwith reference to FIGS. 22 to 26.

FIGS. 22 to 26 are cross sectional views corresponding to the crosssectional structure of the phase shift mask shown in FIG. 1.

Referring to the figures, as in the second and third embodiments, phaseshifter film 4 is formed on quartz substrate, which is made of amolybdenum silicide oxide film, a molybdenum silicide nitride oxidefilm, a chromium oxide film, a chromium nitride oxide film, or achromium carbide nitride oxide film.

Thereafter, an antistatic film 6 of approximately 100-500 Å in thicknessis formed on phase shifter film 4. When the film material of the phaseshifter film belongs to the Mo family, a molybdenum film is to be formedas antistatic film 6. When it belongs to the Cr family, a chromium filmis to be formed as antistatic film.

This is because phase shifter film 4 of a molybdenum silicide oxide, amolybdenum silicide nitride oxide, a chromium oxide, a chromium nitrideoxide, or a chromium carbide nitride oxide, formed in the aforementionedmethod does not have conductivity.

With regard to Cases C-1 to C-3 described in connection with the thirdembodiment, since a chromium oxide film formed in the above cases hasconductivity, the antistatic film is not required.

Subsequently, an electron beam resist film of approximately 5000 Å inthickness is formed on antistatic film 6.

Referring to FIG. 23, resist film 5 having a desired resist pattern isformed by exposing to electron beams and developing a prescribed portionof electron beam resist film 5.

Referring to FIG. 24, sequential dry etching of antistatic film 6 andphase shifter film 4 is performed using a CF₄ +O₂ gas, with electronbeam resist film 5 as a mask when antistatic film 6 belongs to the Mofamily.

Referring to FIG. 25, resist film 5 is removed using O₂ plasma or thelike. Referring to FIG. 26, antistatic film 6 is removed by etching withetching liquid (a mixture of ammonium ceric nitrate and perchloric acid)or the like.

The phase shift mask is thus completed.

Referring to FIG. 24 again, when antistatic film 6 belongs to the Crfamily, sequential dry etching of antistatic film 6 and phase shifterfilm 4 is performed with a CH₂ Cl₂ +O₂ gas, a Cl₂ +O₂ gas, or Cl₂ gas,with electron beam resist film 5 as a mask.

Referring to FIG. 25, resist film 5 is removed using O₂ plasma or thelike. Referring to FIG. 26, antistatic film 6 is removed by etching withsulfuric acid.

The phase shift mask is thus completed.

Although an antistatic film of molybdenum is formed in the case of aphase shift mask belonging to the Mo family, and an antistatic film ofchromium is formed in the case of a phase shift mask belonging to the Crfamily in etching of the phase shift mask, the present invention is notto limited to this, and the same effects can be obtained by using anantistatic film of Mo for a phase shift mask belonging to the Cr family,or using an antistatic film belonging to the Cr family for a phaseshifter film belonging to the Mo family.

As describe above, providing a molybdenum film in the manufacturingprocess of the phase shift mask, an antistatic effect in irradiation oflight beams can be obtained. This also serves as a light reflecting filmfor a position detector of optical type.

Although a molybdenum film or a chromium film is used as an antistaticfilm in the fourth embodiment, the same effects can be obtained by usinga film of W, Ta, Ti, Si, Al or the like, or alloys thereof.

Description will be now made of methods of detecting a defect andrepairing the same, when a remaining defect (an opaque defect) 50 or apin hole defect (a clear defect) 51 occurs on the phase shift maskformed in the first to third embodiments, as shown in FIG. 27.

First, utilizing a light transmit type defect detection apparatus(manufactured by KLA, 239HR type), the presence of a defect in amanufactured phase shift mask is checked by comparing chips.

In this defect detection apparatus, the check is carried out with lightemitted from a mercury lamp.

As a result, a remaining defect in which the phase shifter film remainson the pattern to be etched, and a pin hole defect in which the phaseshifter film to be left is eliminated because of a pin hole or a lackedshape are detected.

These defects are then repaired. The remaining defect is repaired by alaser blow repair apparatus with a YAG laser, as in a conventionalphotomask.

Another method of removing the remaining defect is to performassist-etching by FIB with a gas for sputter etching.

The pin hole defect is repaired by burying the pin hole defect portionthrough deposition of a carbon film 52 by FIB assist deposition method,as in a conventional photomask.

A good phase shift mask can thus be obtained without carbon film 52being peeled off even when the repaired phase shift mask is washed.

Description will now be made of an exposure method using theabove-described phase shift mask.

When the phase shift mask is used, a phase shifter film is formed withthe thickness of approximately 1500 Å to 2000 Å as shown in filmthickness dimension (ds) of Table 2 to Table 4 and Table 6 to Table 8.Since the phase shifter film is formed with the thickness approximatelyhalf of that of a conventional phase shifter film, it is possible toconvert oblique exposure light included in exposure light by 180° asshown in FIG. 28.

As a result, as shown in FIG. 29, when a contact hole of 0.4 μm is to beopened, for example, it is possible to allow focus tolerance of 1.2 μm.In the case of a conventional photomask, as shown in FIG. 30, when acontact hole of 0.4 μm was to be opened, focus offset of only 0.6 μm wasallowed.

In an exposure apparatus having coherence of 0.3 to 0.7 favorably0.5-0.6, as shown in FIG. 31, it is possible to substantially improvedepth of focus as compared to the case of the conventional photomask.

FIGS. 29 and 30 show the relationship between contact hole size andfocus tolerance in the case where a reduction and projection exposureapparatus having a reduction ratio of 5:1 is used. However, it ispossible to obtain similar effects with a reduction and projectionexposure apparatus having a reduction ratio of 4:1 or 3:1, or projectionexposure apparatus having a reduction ratio of 1:1. It is possible toobtain similar effects not only with a projection exposure apparatus butalso with a contact exposure apparatus and a proximity exposureapparatus.

In addition, it is possible to obtain similar effects that a krF laser(λ=243 nm), an i-line (λ=365 nm) and a g-line (λ=436 nm) is using asexposure light.

As described above, according to the exposure method using the phaseshift mask in this embodiment, since it is possible to preventoccurrence of exposure failure, it is possible to improve the yield inthe manufacturing steps of a semiconductor device. The exposure methodcan be effectively used in the manufacturing steps of semiconductordevice such as a DRAM of 4M, 16M, 64M, 256M, an SRAM, a flash memory, anASIC (Application Specific Integrated Circuit), a microcomputer, andGaAs. Furthermore, the exposure method can be well used in themanufacturing steps of a unitary semiconductor element and a liquidcrystal display.

Now, a fourth embodiment in accordance with the present invention willbe described below. The above-described phase shift masks of attenuationtype in the first through third embodiments have the transmittance setto 5-40%. In particular, phase shift masks of attenuation type havingthe transmittance of 5-15% are actually employed for development andmanufacture of semiconductor devices.

Improvement in resolution of a phase shift mask of attenuation typedepends on the transmittance of a phase shifter film. The higher thetransmittance is, the more greatly resolution improves. Therefore, aphase shift mask of attenuation type having a high transmittance isdesired. However, with the higher transmittance, a greater amount oflight transmits through the phase shifter film. As a result, a resistfilm is undesirably exposed to the light beams transmitting through thephase shifter film a plurality of times (foggy exposure).

The resist film which should not be etched is reduced in thickness, whena positive resist film is used, by the multiple exposure, and thereforethe pattern of the resist film is destroyed.

This effect of multiple exposure also depends on the contrast of theresist film.

Generally, the upper limit of the transmittance at which the resist filmis not affected by multiple exposure is 15%, when the resist film usedin the manufacturing steps of a semiconductor device is employed. Theupper limit of the transmittance can be made higher by improvement incontrast of the resist film and other processes.

New problems have arisen as phase shift masks of attenuation type areturned into practical use and widely applied to the manufacturingprocesses of semiconductor devices.

First, although a resist film usually employed has a thickness ofapproximately 1 μm, a resist film having a thickness of approximately 2μm is required for some manufacturing processes.

When a positive resist film is exposed to the light having a portionwith the thickness of 1 μm and another with the thickness of 2 μm, whichtwo portions have the same sensitivity, the portion with the thicknessof 2 μm requires a greater amount of exposure light to form a pattern.With the greater amount of exposure light, a problem of multipleexposure of the resist film is generated by the light transmittingthrough the phase shift film, as described above.

Referring to FIGS. 32 and 33, description will now be made of anotherproblem that by side lobes (b) (first-order diffraction light) of thelight beams (a) transmitting through light transmit portion 10 with ahole pattern, a surrounding region of the hole pattern is exposed to thelight. For example, referring to FIGS. 34 and 35, at a resist film 110formed on a semiconductor substrate 100 an unnecessary hole 110b isformed around a hole 110a originally designed to be opened.

Although one might consider reducing the transmittance of theattenuation type phase shift mask as much as possible in the range of5-40%, it is evident that the effects of multiple exposure and sidelobes described above show up even with the transmittance of 5%

For example, when a phase shift mask of attenuation type is used whichhas a negative line pattern 10 as shown in FIG. 36 for forming a storagenode or the like, the following problem is generated.

When the transmittance of the phase shifter film is 5% or more and theresist film is exposed to light using a mask pattern as shown in FIG.36, a depressed portion or hole 110b is generated at the central portionof resist pattern 110 as shown in FIG. 37. This is because the sidelobes generated around resist pattern 110 overlap with each other at thecentral portion of resist pattern 110, thereby exposing the resist filmto the light.

This effect is present even with the phase shifter having thetransmittance of 5%, though the effect is small.

As a result, if etching, which is the next step, is performed by usingthis resist film, the problems of etching failure and a drop in accuracyof the dimension of the etched material are generated due to a change inthe shape of the pattern of the resist film.

A fourth embodiment is conceived for solving these problems andobtaining a phase shifter film which has such a transmittance as toimprove effects of the phase shift mask of attenuation type, and a phaseshift mask of attenuation type having such a phase shifter film.

It has been found that the effects of the above mentioned problems arereduced sharply and significantly if the transmittance of the phaseshifter film is lowered to 5% or less. The effect becomes considerablysmall with transmittance of less than 5%, and especially when thetransmittance is 4% or less, the above-described problems do not occurat all.

However, if the transmittance of the phase shifter film is lowered, itbecomes close to that of the conventional photomask shown in FIG. 44A,whereby improvement in resolution becomes small.

In this regard, FIG. 38 shows the relation between resolution and thetransmittance when the transmittance of the phase shift mask is lessthan 5%. As can be seen from the result shown in FIGS. 38 and 39,regarding the transmittance of the phase shifter film being less than5%, the transmittance of 2% or more is required for improvement inresolution.

Therefore, the range of the transmittance for solving the aforementionedproblems and also obtaining effects of a phase shift mask of attenuationtype is required to be at least 2% and less than 5%.

Now, a method of manufacturing a phase shift mask of attenuation typeincluding a phase shifter film which has the transmittance of at least2% and less than 5% and the phase angle of 180° and which is made of asingle material.

First, an example in which a phase shifter film made of molybdenumsilicide oxide and molybdenum silicide nitride oxide is used will bedescribed below.

The sputtering device similar to the one shown in FIG. 7 is used forforming the above-mentioned film.

Referring to FIG. 8 and Table 2, which have been already describedabove, when krF laser is used as exposure light, the transmittance of atleast 2% and less than 5% required for a phase shifter film is obtainedin M-2, M-3, M-7, M-9, and M-14 to M-16.

Referring to FIG. 9 and Table 3 showing the cases of exposure light ofthe i-line, it can be seen that the transmittance T of at least 2% andless than 5% required for a phase shifter film is obtained in M-4 toM-7.

Referring to FIG. 10 and Table 4 showing the cases of exposure light ofthe g-line, it can be seen that the transmittance T of at least 2% andless than 5% required for a phase shifter film is obtained in M-4 toM-6.

As a result, the film formed in M-2 to M-7, M-9, and M-14 to M-16 can beemployed as a phase shifter film having transmittance T of at least 2%and less than 5%.

FIG. 40 is a graph showing the above cases with respect to gas flowratios. In the graph shown in FIG. 40, respective rates of argon, oxygenand nitrogen in cases M-1 to M-17 are described.

In this graph, a point of a mixed gas in each case is plotted, whereinthe base of the triangle indicates the flow ratio (%) of argon, the leftoblique side thereof indicates the flow ratio (%) of oxygen, and theright oblique side thereof indicates the flow ratio (%) of nitrogen. Inaccordance with the result shown in FIGS. 8-10 and Tables 2-4, a casethe film of which is applicable as a phase shifter film havingtransmittance T of at least 2% and less than 5% is indicated by acircle, while a case the film of which is not applicable to a phaseshifter film having the transmittance of at least 2% and less than 5% isindicated by a cross.

As can be seen from the graph in FIG. 40 and from Table 1, a mixed gasfor forming a molybdenum silicide oxide film applicable as a phaseshifter film with the transmittance T of at least 2% and less than 5%includes 73-76% argon and 24-27% oxygen by volume.

A mixed gas for forming a molybdenum silicide nitride oxide filmapplicable as a phase shifter film with transmittance T of at least 2%and less than 5% includes 57-79% argon, 7-18% oxygen and 4-32% nitrogenby volume.

As described above, in the phase shifter mask in accordance with thepresent invention, a phase shifter film forming a second light transmitportion and having the transmittance of at least 2% and less than 5% isconstituted only of molybdenum silicide oxide film or a molybdenumsilicide nitride oxide film.

In the manufacturing process thereof, a molybdenum silicide oxide or amolybdenum silicide nitride oxide is formed to a prescribed filmthickness by a sputtering method, and thereafter, a prescribed etchingis performed, whereby the second light transmit portion is formed.

Consequently, a phase shifter film can be formed with a conventionalsputtering apparatus, and additionally, probabilities of defects anderrors in a pattern dimension can be reduced because etching process isrequired only once.

Description will be made of an example in which either of a chromiumoxide film, a chromium nitride oxide film, and chromium carbide nitrideoxide film is employed as a phase shifter film.

The process for manufacturing the phase shift mask in which either of achromium oxide film, a chromium nitride oxide film, and a chromiumcarbide nitride oxide film is employed as a phase shifter film isidentical to the process shown in FIGS. 12-15, and therefore thedescription thereof will not be repeated.

Description will be made of a formation of a phase shift film made of achromium oxide film, a chromium nitride oxide film, and a chromiumcarbide nitride film will be described.

Table 5 shows the pressure in vacuum vessel, the deposition rate and thefilm material in each of the cases in which various flow ratios of amixed gas are set. A phase shifter film of a chromium oxide is to beformed in cases C-1 to C13, a phase shifter film of a chromium nitrideoxide is to be formed in cases C-14 to C-26, and a phase shifter film ofa chromium carbide nitride oxide is to be formed in cases C-27 to C-30.

Tables 6-8 show the transmittance, the n value and the k value in theoptical constant (n-i·k) and the film thickness d_(s) for converting aphase of exposure light by 180° in the cases employing a krF laser(λ=248 nm), and i-line (λ=365 nm) and a g-line (λ=436 nm), respectively.

In Tables 6-8, the film thickness d_(s) can be obtained from thefollowing:

    d.sub.s =λ/2(n-1)                                   (2)

where λ is a wavelength of exposure light, and n is a value in theoptical constant.

FIGS. 16-18 are graphs of data shown in Tables 6-8. The horizontal axisindicates the n value in the optical constant, the left vertical axisindicates the k value in the optical constant, and the right verticalaxis indicates the film thickness d_(s).

The transmittance T is also shown in FIGS. 16 to 18.

Referring to FIG. 16 and Table 6 showing the case of exposure light ofthe krF laser, it can be seen that the transmittance T of at least 2%and less than 5% required for a phase shifter film is obtained in C13,and C-25.

Referring to FIG. 17 and Table 7 showing the case of exposure light ofthe i-line, it can be seen that the transmittance T of at least 2% andless than 5% required for a phase shifter mask is obtained in C-17 andC-29.

Referring to FIG. 18 and Table 8 showing the case of exposure light ofthe g-line, it can be seen that the transmittance T of at least 2% andless than 5% required for a phase shifter film is obtained in C-21, C-23and C-26.

As a result, the films formed in cases C13, C-17, C-21, C-23, C-25, C-26and C-29 can be employed as a phase shifter film having transmittance Tof at least 2% and less than 5%.

FIGS. 41-43 are graphs showing the above cases based on the relation ofgas flow ratios in the mixed gas Ar+O₂ ; Ar+O₂ +N₂, Ar+NO, Ar+O₂ +CH₆,respectively. The graph shown in FIG. 41 shows the rates of argon,oxygen and nitrogen in Cases C-1 to C-18.

In this graph, a point of a mixed gas in each case is plotted, whereinthe base of the triangle indicates the flow ratio (%) of argon, the leftoblique side of the triangle indicates the flow ratio (%) of oxygen, andthe right oblique side of the triangle indicates the flow ratio (%) ofnitrogen.

In accordance with the result in FIGS. 16-18 and Table 5, a case thefilm of which is applicable as a phase shifter film having thetransmittance T of at least 2% and less than 5% is indicated by acircle, while a case the film of which is not applicable as a phaseshifter film is indicated by a cross.

As can be seen from the graph in FIG. 41, a mixed gas for forming achromium oxide film applicable as a phase shifter film havingtransmittance T of at least 2% and less than 5% includes 95-96% argonand 4-5% oxygen by volume.

A mixed gas for forming a chromium nitride oxide film applicable as aphase shifter film having transmittance T of at least 2% and less than5% includes 82-83% argon, 4-5% oxygen, and 12-13% nitrogen by volume.

FIG. 42 is a graph showing the rates of argon and NO in Cases C-19 toC-26. In accordance with the result in FIGS. 16-18 and Table 5, a casethe film of which is applicable as a phase shifter film with atransmittance T of at least 2% and less than 5% is indicated by acircle, while a case the film of which is not applicable as a phaseshifter film is indicated by a cross.

FIG. 43 is a graph showing the rates of argon and methane in Cases C-27to C-30.

In the graph, a point of a mixed gas in each case is plotted, whereinthe base of the triangle indicates the flow ratio (%) of argon, the leftoblique side thereof indicates the flow ratio (%) of oxygen, and theright oblique side thereof indicates the flow ratio (%) of methane.

In accordance with the result in FIGS. 16-18 and Table 5, a case thefilm of which is applicable as a phase shifter film is indicated by acircle, while a case the film of which is not applicable as a phaseshifter film is indicated by a cross.

As can be seen from the graphs in FIGS. 41-43 and Table 5, a mixed gasfor forming a chromium nitride oxide film applicable as a phase shifterfilm includes 75-87% argon, and 12-25% nitrogen monoxide by volume.

A mixed gas for forming a chromium carbide nitride oxide film applicableas a phase shifter film includes 78-79% argon, 12-14% oxygen, and 8-9%methane by volume.

As described above, in this phase shifter film, a second light transmitportion is constituted only of a film of a chromium oxide, a chromiumnitride oxide, or a chromium carbide nitride oxide, having thetransmittance of at least 2% and less than 5%.

The above-described film is formed to a prescribed film thickness by asputtering method, and thereafter, a prescribed etching is performed, sothat the second light transmit portion is formed.

Consequently, a phase shifter film can be formed with a conventionalsputtering apparatus, and probabilities of defects and errors inexposure dimension can be reduced since etching process is required onlyonce.

Although an oxide and a nitride oxide of molybdenum silicide, and anoxide, a nitride oxide, and a carbide nitride oxide of chromium are usedas the second light transmit portion as described above, it is notlimited thereto, and an oxide and a nitride of metal, and an oxide and anitride oxide of metal silicide may be used.

In the phase shift mask in accordance with the present invention, asecond light transmit portion is made only of a single material film.

Additionally, in the manufacturing process of the phase shift film, thesecond light transmit portion is formed by forming a prescribe phaseshifter film on a substrate transmitting exposure light by a sputteringmethod, and thereafter, performing a prescribed etching.

This enables formation of a phase shifter film at a single step with aconventional sputtering apparatus. Moreover, since etching process isrequired only once, probabilities of defects and errors in the patterndimension will be decreased, so that a phase shift mask of high qualitycan be provided.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and it not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A method of detecting a remaining defect (blackdefect), or a pin hole defect (white defect) in a second lighttransmission portion of a phase shift mask including a substratetransmitting exposure light and a phase shift pattern having a firstlight transmission portion exposing said substrate and said second lighttransmission portion having a phase of transmitted exposure lightconverted by 180° with respect to the phase of exposure lighttransmitted through said first light transmission portion, having atransmittance of at least 2% and less than 5% and being formed of asingle film selected from the group consisting of an oxide film of ametal, a nitride oxide film of a metal, an oxide film of metal silicideand a nitride oxide film of metal silicide,which method comprisesdetecting a defect by a chip comparison method using a mercury lamp as alight source.
 2. A method of repairing a remaining defect (black defect)generated in a second transmission portion of a phase shift maskincluding a substrate transmitting exposure light and a phase shiftpattern formed on a main surface of the substrate, said phase shiftpattern having a first light transmission portion exposing thesubstrate, and said second light transmission portion having a phase oftransmitted exposure light having a phase converted by 180° with respectto the phase of exposure light transmitted through said first lighttransmission portion, having a transmittance of at least 2% and lessthan 5%, and formed of a single film selected from the group consistingof an oxide film of a metal, a nitride oxide film of a metal, an oxidefilm of metal silicide, and a nitride oxide film of metal silicide,whichmethod comprise removing the remaining defect (black defect) in saidsecond light transmission portion by sputter-etching using a YAG laseror FIB.
 3. A method of repairing a pin hole defect (white defect)generated in a second light transmission portion of a phase shift maskincluding a substrate transmitting exposure light and a phase shiftpattern formed on a main surface of the substrate, said phase shiftpattern having a first light transmission portion exposing the substrateand said second light transmission portion having a phase of transmittedexposure light converted by 180° with respect to the phase of exposurelight transmitted through said first light transmission portion, havinga transmittance of at least 2% and less than 5%, and being formed of asingle film selected from the group consisting of an oxide film of ametal, a nitride oxide film of a metal, an oxide film of metal silicideand a nitride oxide film of metal silicide,which method comprisesfilling the pin hole defect (white defect) generated in said secondlight transmission portion by deposition of a carbon-based filmemploying an FIB assisted deposition method.